Single-crystalline α-MnO2 and β-MnO2 nanorods were prepared directly by facile hydrothermal process at 150 ℃ and 220 ℃, respectively. The as-synthesized α-MnO2 and β-MnO2 nanorods were investigated by XRD, TEM, SEM, and EDS. The temperature was found to play important roles in controlling the synthesis of α-MnO2 and β-MnO2 nanorods.